[DRAFT] [REFACTOR] Upgrade Pydantic to v2

[jfcalvo]

Description

This is a draft to make visible the changes that we are doing in order to update Pydantic to v2.

Test suite progress:

1. ==== 402 failed, 897 passed, 17 skipped, 1582 warnings in 189.12s (0:03:09) ====
2. ==== 207 failed, 1092 passed, 17 skipped, 1640 warnings in 186.83s (0:03:06) ====

Refs https://github.com/argilla-io/argilla/issues/4935

Type of change

• Refactor (change restructuring the codebase without changing functionality)

How Has This Been Tested

Checklist

• I added relevant documentation
• I followed the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• I confirm My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)